Models were developed using normal human bronchial epithelial (NHBE) cells for studying compounds reputed to be cocarcinogens and/or tumor promoters in animal models. Compounds were tested for cytotoxicity by colony forming efficiency (CFE) and population doubling time (PDT) assays. The compounds were then screened by using concentrations that were maximally mitogenic or that caused no more than a 50% decrease in colony forming efficiency of cells exposed for 6 hours. The cells were observed for morphologic changes under phase contrast light microscopy and scanning and transmission electron microscopy and assayed for changes in ornithine decarboxylase (ODC), plasminogen activator (PA), and aryl hydrocarbon hydroxylase (AHH) activity, and cross-linked envelope (CLE) formation. Twenty-eight compounds have been tested thus far for mitogenicity or cytotoxicity, and most have been characterized by the biochemical assays. As these initial studies are completed, selected, compounds will be used for in vitro carcinogenesis experiments and to further investigate their mechanisms of action.